1. Field of the Invention
The present invention relates to a test method of a subscriber line transmission system, and particularly relates to a testing method so adapted as to be capable of testing a subscriber line and a subscriber circuit simultaneously.
A subscriber line transmission system is one which concentrates a plurality of subscriber terminals and connects them to an analog exchange through a PCM line. When a subscriber terminal exists at a place remote from any exchange, the subscriber line transmission system is used for connecting such subscribers with an analog exchange.
Development of communication networks in recent years has enhanced functions of subscriber line transmission systems. Keeping step with this, a need is increasing for various tests for maintenance of a subscriber line transmission system. However, a test for each circuit takes much time in a subscriber line test. Therefore, a method in which a test can be efficiently achieved in a short time is required.
2. Description of the Related Art
When an exchange office with a switching system has a plurality of subscribers, who are at places remote from the exchange office, a remote terminal (RT) is provided at the subscriber side, and a central office terminal (COT) is provided in the exchange. The terminals are connected through an optical transmission line comprising a PCM circuit.
Then, in the RT, the subscriber lines corresponding to the subscribers are concentrated, and a signal of each subscriber is multiplexed and converted into a PCM signal. At the same time, in the COT, the subscriber lines from the switching system corresponding to the subscribers are concentrated, and a signal of each subscriber line is multiplexed and converted into a PCM signal.
With the above arrangement, it becomes possible to reduce the cost of providing a line between the switching system and each subscriber, and at the same time to prevent a loss of a signal in a transmission line even when the distance between a subscriber and the exchange office is large.
Conventionally, using a subscriber line tester (SLT), a subscriber line transmission system is adapted to permit testing and measurement of voltage (AC and DC), insulating resistance and capacitance values of subscriber lines in a state where the subscriber lines are separated from the subscriber line circuits. In this test method, for each subscriber line, the voltage, resistance and capacitance of the subscriber line are measured, and therefore, a significantly long testing time is needed for each line
Also, an arrangement is provided so that the test of the subscriber line circuits can be achieved for one subscriber at a time, by using a measuring device. In a subscriber line transmission system, the testing of the subscriber line and the test of the subscriber line circuits are conventionally done individually, so a long time is needed for testing.
Thus, there is a problem that it takes a long time for the subscriber line test and the subscriber circuit test and a test cannot be done efficiently in a conventional subscriber line transmission system.